A preliminary exploration of interpopulation variation in facial soft tissue thicknesses in Indigenous Western Canada.

Targeted action to question, reexamine, and improve current forensic techniques and capabilities is needed to address the ongoing national crisis of Missing and Murdered Indigenous Persons. While a number of authors have suggested the application of population-specific facial soft tissue thickness (FSTT) tables is necessary when completing a facial approximation, others advocate for the application of universal standards. At the time of publication, there are no existing FSTT tables for the Indigenous populations of Western Canada which has resulted in the application of reference standards specific to other populations. This raises the important question: how important are population-specific reference standards? To evaluate whether there is an advantage to population-specific models, this study considered C-Table reference data representing Black American (Manhein et al., 2000), White American (Manhein et al., 2000), and Caucasoid (Australian; Stephan and Preisler, 2018; Stephan and Sievwright, 2018) populations. The results of a k-means clustering analysis (k = 4, sil = 0.14) of these data, in conjunction with additional testing examining FSTT variation by population, suggested that it is possible there is variation within the table that is attributable to biogeographic ancestry, sex, and body mass index (BMI). Next, original data from a Western Canadian Indigenous population (including self-identifying First Nations and Métis participants, n = 10) was collected and compared FSTT tables originating from other North American populations, including Mi’kmaq (Peckmann et al., 2015), Black American (Manhein et al., 2000), White American (Manhein et al., 2000), and Southwestern Native American (Rhine, 1983 cited in Taylor, 2001) groups. Data for the Western Canadian Indigenous sample (n = 10) were collected using the Philips Epiq 7c ultrasound system with a Philips L12-3 broadband linear array transducer (12 - 3 MHz). Limited evidence of significant interpopulation variation was found. Additionally, it was found that the Western Canadian Indigenous FSTT values are not likely to be significantly different from the 2023 T-Table, which is a compilation of existing reference data representing > 130 past FSTT studies (Hona and Stephan, 2023). Intrapopulation variation within the Western Canadian Indigenous sample was also considered and it was found that there is evidence of significant variation attributable to BMI but not age. Multidimensional scaling (MDS) plots were used to visualize the complex spatial relationships between Western Canadian Indigenous individuals, which were interpreted using known population histories and self-identified ancestry to provide context. Across each section of this work, limited evidence of true biogeographic variation in FSTT was found. However, this study introduced a novel framework for exploring Indigenous ancestries in a colonial context using relationality as an indigenist research framework. Future researchers are encouraged to continue to explore decolonial strategies for exploring and describing Indigenous ancestries.

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